To move an object in space, manipulation arms are known, the articulations of which are mounted in series and those the articulations of which are mounted in parallel. These arms are also called robots.
The robots of these serial articulation types have a disadvantage in that they are relatively heavy and thus have a high inertia which prevents them from working at high rates.
The so-called parallel robots enable much faster displacements but the amplitude of the movements is limited.
The invention relates to a so-called parallel robot.
Such robots are more particularly known from EP-A-250 470, EP-A 1.129.829, WO-A-0035640 including three actuators, including a fixed part and a movable part having only one degree of freedom with respect to the fixed part, with each movable part being connected to a movable head through linking members.
The device is shaped as a deformable pyramid with triangular bases.
Each actuator is an electric motor the rotation axis of which is coupled to an arm (the movable part) pivoting about the actuator rotation axis.
The private axes of the arms form a triangle and the linking members are respectively hinged on a head (the small base) and the corresponding movable part.
The articulations of such linking members to the arms as well as to the head are given two degrees of freedom.
Then, the orientation and the direction of the head are not modified in space.
Often, a telescopic transmission gripping device is mounted at the centre of the system.
A central support carries the actuators. This central support substantially has the same dimensions as defined by the three pivoting axes.
The rotation bearings of the pivoting arms are saddled on the pivot axes and are, each, half inscribed in the surface defined by the pivoting axes of the arms.
The arms are radial, at least in their end parts, and extend to the outside of the central support. The displacement amplitude is minimised by the extent of the support which must have a sufficient size to carry the actuators and often a fourth arm which is used as a gripping device connecting the larger base to the smaller base. The displacement amplitude is related to the useful length of the arm.
The overall dimensions are defined by the circle going through the ends of the arms when the system is in neutral position and the arms are then in the same plane, here a horizontal plane.
The axes of the arms are generally mounted so that the longitudinal axes of said arms intersect at the centre of the triangle formed by the pivot axes.
It should be understood that the larger the support for given overall dimensions, the smaller the length of the arms. Thus for the overall dimension of approximately 550 millimeters in radius, the length of the arm is 350 millimeters, the working height obtained is thus of the order of 300 millimeters and the diameter of the working area is of the order of 1,100 millimeters.
To increase the length of the arms for given overall dimensions, the size of the support should be reduced but it depends on the size of the actuators and in the configurations known, it cannot be much reduced.
Now, the overall dimensions must also be a factor taken into account for positioning said robots. In addition, reducing the size support also means for some of the possible positions of the arms, reducing the rigidity of all the movable members of the robot. Such constraints result in the present definition of the state of the art which is composed of parallel robots having a large fixed base and having arms radiating to the outside.